1. Field of the Invention
The present invention relates to aqueous pigment pastes comprising hydrophobically modified polyaspartic acid derivatives as dispersants. The present invention relates in particular to the use of hydrophobically modified polyaspartic acid derivatives as dispersants for preparing aqueous pigment pastes.
2. Prior Art
Pigment pastes for the purposes of the present invention embrace pastes of organic and/or inorganic pigments or fillers in aqueous media. In the preparation of paints and coating materials, wetting agents and dispersants make it easier to incorporate pigments and fillers, which are important formulation constituents as they determine significantly the visual appearance and the physicochemical properties of coatings. To best exploit their effects it is necessary, firstly, for these solids to be distributed uniformly in coating materials and paints and, secondly, for the distribution, once achieved, to be stabilized. Indeed, during the preparation and processing of aqueous pigment pastes, numerous problems may arise:
difficulties in incorporating the pigments PA0 high viscosities of ink pastes, paints and coating materials PA0 sedimentation PA0 vertical migration of pigments (floating) PA0 horizontal migration of pigments (flooding) PA0 low degree of gloss PA0 low hiding power PA0 inadequate depth of color PA0 poor reproducibility of shade PA0 excessive tendency of coating materials to run PA0 R.sup.2 is one or more radicals from the group consisting of alkali metals, alkaline earth metals, hydrogen and ammonium, [NR.sup.5 R.sup.6 R.sup.7 R.sup.8 ].sup.+, where PA0 R.sup.5 to R.sup.8 independently of one another are hydrogen, alkyl or alkenyl of 1 to 22 carbon atoms or hydroxyalkyl of 1 to 22 carbon atoms and 1 to 6 hydroxyl groups, PA0 R.sup.3 is identical or different, straight-chain or branched, saturated or unsaturated alkyl or alkenyl radicals R.sup.9 of 6 to 30 carbon atoms or is radicals of the structure --X--R.sup.9, where X is an oligooxyalkylene or polyoxyalkylene chain of 1 to 100 oxyalkylene units, and PA0 R.sup.4 is identical or different, straight-chain or branched, saturated or unsaturated alkyl or alkenyl radicals of 1 to 5 carbon atoms PA0 and at least one radical R.sup.1 must adopt the definition of R.sup.2 and at least one radical R.sup.1 must adopt that of R.sup.3 or R.sup.4 and PA0 the units of the general formula (II) are proteinogenic or nonproteinogenic amino acids and are present in a proportion of not more than 20% by weight based on the copolymeric polyaspartic acid derivatives.
There has therefore been no lack of attempts to provide effective dispersing additives for solids, especially pigments. Examples of dispersing additives which are described as being highly suitable for these purposes are water-soluble, polyisocyanate adducts containing hydrophilic polyether chains (see European Publication No. 0 731 148 A), hydrophilic polyurethane-polyureas (see German Publication No. 44 16 336 A), poly(meth)acrylates (see U.S. Pat. No. 3,980,602 and International Patent Publication No. WO 94/21701 A), and specific polyesters (see International Publication No. WO 94/18260 A).
However, the use of such products is also associated with a large number of disadvantages. For instance, high levels of added dispersing additives are often necessary; the levels of paste pigmentation which can be achieved are unsatisfactorily low; the stability of the pastes and thus the constancy of their viscosity is inadequate--flocculation and aggregation cannot always be avoided; in many cases, following a storage of the pastes, there is also a lack of constancy of shade and of compatibility with various binders. The use of known dispersing additives also in many cases has an adverse effect on the water resistance of coatings; moreover, the undesirable foam which forms during preparation and processing is additionally stabilized. A further criterion, whose importance has increased in recent times in particular, is the environmental compatibility of the additives.
It is an object of the present invention to overcome many of the abovementioned disadvantages and in so doing to exert a positive influence in particular on the viscosity and the development of tinctorial strength during the preparation of the pastes and their processing.